1. Field of the Invention
The present invention relates to a curing apparatus for drying a thermo-setting bonding agent such as a silver paste, etc. applied to plate-form parts such as lead frames, etc.
2. Prior Art
In semiconductor device manufacturing processes, workpieces consisting of dies bonded to lead frames via a thermo-setting bonding agent are heated by a curing apparatus so that the thermo-setting bonding agent is dried to fix the dies to lead frames. Generally, to heat (and drying) the workpieces, heating blocks are used.
If the temperature in the vicinity of the surfaces of the workpieces drops, impurity gases (which are generated by the pyrolysis of the thermo-setting bonding agent) cool down and solidify to form particles. These particles tend to remain on the surfaces of the workpieces, thus decreasing the quality of the finished product. One way to prevent these drawbacks is to blow a high-temperature inert gas to the vicinity of the workpiece surfaces from above, thus preventing the conversion of the impurity gases into particles and cleaning the workpiece. The impurity gases are then discharged and removed.
There are three high-temperature inert gas supply systems in prior art: one-way systems, high-temperature gas chamber systems and pipe systems. In the one-way systems, a high-temperature gas is caused to flow along the surfaces of workpieces from one end, and the gas is discharged from the other end. In the high-temperature gas chamber systems, a high-temperature gas is supplied into a high-temperature gas chamber installed above a workpiece heating area and is then supplied to the surface of workpieces through slits which are formed in the bottom of the high-temperature gas chamber. In the pipe systems, a high-temperature gas is blown into a pipe installed above the workpiece heating area. The gas is supplied to the surfaces of workpieces via holes which are opened in the bottom of the pipes.
The curing devices of the types described above may be found in, for example, Japanese Patent Application Laid-Open ("Kokai") Nos. 63-239957 and 63-316443 and Japanese Utility Model Application Laid-Open ("Kokai") No. 2-8033.
Of the above prior art systems, in the one-way systems, the cleaning efficiency of the workpiece varies depending upon the positional relationship between the workpiece and the flow of the high-temperature gas. More specifically, workpieces near the high-temperature gas inlet are constantly covered by a fresh supply of the high-temperature gas and therefore cleaned well. However, the gas which has flown along the surfaces of the preceding workpieces is supplied onto the workpieces placed near the high-temperature gas outlet. Accordingly, impurities and gases which have been contaminated by the preceding workpieces are blown thereto. As a result, cleaning is not performed well. Since there is a temperature differences at the gas inlet area and the gas discharge area, heat curing obtaining equal quality workpieces cannot be expected.
In the high-temperature gas chamber systems, since a high-temperature gas is blown directly onto the surfaces of the workpieces, gas at a uniform temperature cannot be evenly supplied to each of the workpieces. Thus, it is impossible to obtain workpieces of equal quality.
In the pipe systems, it is difficult to maintain the temperature of the gas inside the pipe constantly. Accordingly, as in the case of the high-temperature gas chamber systems, workpieces of equal quality cannot be obtained. Since the gas is supplied through positionally-fixed holes, the conditions of gas supply change if the lead frames are different in dimensions or spacing between placed on the lead frames is different. Accordingly, stable heating cannot be expected for different types of products.